Split operation
| Split operation | |
|---|---|
| What it is | Transmitting on one frequency while listening on another |
| Main use | Managing pileups on rare DX stations |
| Typical instruction | "Up 5" on SSB; "UP 1" or "UP 2" on CW |
| Radio feature | Split button using two VFOs, A and B |
| Etiquette | |
| Golden rule | Never transmit on the DX station's own frequency |
| Where to call | Within the range the DX station announces |
| Legal limit | The transmitted signal must stay inside the caller's license privileges |
Split operation is the practice of transmitting on one frequency while listening on another. On the HF bands it is the standard way for a rare DX station to handle a pileup, the crowd of stations all calling at once. By listening away from its own transmit frequency, the DX station keeps that frequency clear, so everyone can hear its instructions and the call signs it is working. For the callers, working split is a basic skill: most rare stations and DXpeditions operate this way, and calling them on the wrong frequency is one of the commonest mistakes on the bands.
How it works
A DX station working split announces where it is listening. On SSB, "listening up 5" means it is listening about 5 kHz above its transmit frequency, and "up 5 to 10" means anywhere in that range. On CW the DX station sends "UP" or "UP 2" every few contacts, meaning a kHz or two higher. "Down" is used too, though less often.
The DX station tunes around its announced range, picks out one call sign, and works that station. Then it moves on, often tuning a little higher or lower each time. Spreading the callers across several kilohertz makes individual call signs much easier to pick out than a single wall of signals on one frequency.
Split is also used where band allocations differ between countries, so two stations can't transmit on the same frequency, and it underlies the frequency offsets used by repeaters and satellites, though those are seldom called "split."
Setting up the radio
Most HF transceivers have two VFOs (variable-frequency oscillators), usually labeled A and B. In normal use the radio receives and transmits on the same VFO. Pressing Split makes the radio receive on one and transmit on the other. A typical setup:
- Tune VFO A to the DX station's frequency.
- Press A=B (or A/B copy) so both VFOs start on the same frequency, mode and filter.
- Set VFO B to the listening frequency, for example 5 kHz higher.
- Turn split on, and check the display to confirm which VFO will transmit.
Many radios have a quick-split key that does steps 2 to 4 at once, using a preset offset. Radios with a second receiver can listen to both frequencies at once, the DX station in one ear and the pileup in the other, which makes it easier to find where the DX station is actually listening. Before transmitting, many operators press the transmit-frequency monitor button (often labeled TF-SET or XFC) to hear the frequency they are about to call on.
Working a split pileup
- Listen first. Find the station the DX is working by tuning the pileup. A caller who hears the last station worked knows exactly where the DX is listening, and can call at or just above that spot.
- Call briefly. Give your full call sign once or twice, then listen. Long calls cover up the DX station's reply.
- Follow instructions. If the DX asks for one area, or moves its listening range, follow along.
- Stay inside your privileges. The legal requirement applies to the transmit frequency, not the DX station's. A General licensee calling "up 1" on a DX station near a band edge must check that the transmitted signal is within General privileges.
DX cluster spots often include the split in the comment, such as "UP 2" or "QSX 14.205" (QSX meaning "I am listening on"). Spots are a convenience, not a guarantee; the DX station may have moved since the spot was posted.
Etiquette
The cardinal rule is never to transmit on the DX station's own frequency. A caller who forgets to turn on split lands right on top of the DX station, blocking it for everyone. The opposite mistake is just as common: the chorus of "up, up!" or "you're on his frequency" that follows adds more noise to the frequency that should be kept clear. The courteous response is silence. More on pileup manners is under Operating etiquette.
On FT8, DXpeditions often use a "Fox and Hound" mode with its own split arrangement, in which callers transmit higher in the audio passband than the DX station. WSJT-X also has an unrelated "Split Operation" setting that shifts the radio's frequency to keep transmitted audio tones clean; it is not used for pileups.